The light may be used, for example, for traffic lights, which are present at road connections, junctions, pedestrian crossings, various surfaces of a vehicle (e.g vehicles with rubber tire, tracked vehicles and rail vehicles) and other locations where the traffic is required to be controlled. The light may deliver signals via universal color codes in order to regulate traffic.
Until the development of LED technology, traffic lights were produced with incandescent lamp and/or halogen lamp technology. In traffic lights with incandescent and halogen lamps, bright reflective surfaces are used, which direct the light according to any desired angles. Moreover, in order to obtain a homogeneous intensity on the front surface of the lamp, the light source is required to be located at a certain distance from the lens. For this reason, lights with more depth and bigger dimensions were produced. In addition, due to the reflective surfaces used, solar rays may reflect back and reduce the contrast ratio.
LEDs, which were introduced for use with the advance of semiconductor technology, have begun to provide the same light intensity as that given by conventional light sources using much less energy. Further, their small size, longer service lifetime and inexpensive price enables them to be used more efficiently as compared to conventional lamps.
It is possible to form a thinner structure by using a large number of low power LEDs directly arranged on the front surface of a lamp, in order to display information in the traffic lights. However, in order for LEDs to become less affected by the ambient conditions and to achieve the desired angles, colors, intensity and contrast values, it is more appropriate to use the LEDs together with a lens or a series of lenses with protective and optical features.
In the application of high power LEDs, a reduced number of LEDs were positioned at the focal plane of a Fresnel lens. In this way, it becomes possible to gather the intensity from the focal plane in the form of parallel light beams from each individual LED, the total amount of light being within an acute angle with the axis of the Fresnel lens. On the other hand, as is the case with halogen and incandescent lamps, lights with more depth and bigger dimensions were also formed. In front of the Fresnel lens, an outer lens may be used, which distributes the parallel light beams through suitable angles. Rays passing through two different lens surfaces lose their efficiency to some extent, as a result of reflection on each surface.
The Fresnel lens being employed is not able to gather the light with sufficient efficiency and is not able to achieve parallel light beams in the desired manner. For this reason, for example as in the patent no. US2005/0286145 A1, suitable geometries are formed for each angle of radiation.
In traffic lights that operate directly under sun light, it may be required to reduce the back reflection of the sun light in order to increase the contrast value.
It may also be useful to use colored lenses to increase contrast. The lenses may be manufactured with the same color as the color of radiation, thereby enabling the other colors in the solar color spectrum to be absorbed by the lens. Radiation sources that are not monochromatic have a certain wavelength range. It is quite difficult to produce colored lenses without optical absorption in the wavelength range of the light source. For this reason, a significant portion of the light source energy may be lost due to exposure to absorption in the colored lens applications.
Moreover, colored lenses may shine in their own colors when exposed to intense solar light and this may misguide drivers.
Antireflection coatings may also be used on the lens surface. Even though sufficient results are obtained in the calculated wavelength range by this method, no efficient results may be obtained for solar light having a broad spectral range and a wide range of angles of incidence. Multi-layer coatings must be made for a wider wavelength range, but this method is quite expensive. The coatings are also influenced by the weather conditions and may in time begin to peel from the lens surface and lose their effectiveness.
In U.S. Pat. No. 8,152,339 B2, a lightpipe structure is applied on a circular surface, the radiation source is located at the center of the lightpipe and a secondary lens is used in front of the lightpipe. Furthermore, in the same patent, a circular surface is illuminated by a single radiation source from the side surface. However, in this method, a secondary lens in front of the lightpipe is needed in order to provide the homogeneity of the radiation and it may not be possible to obtain a sufficiently homogeneous illumination of the surface by the light emitted from a single source.
Further, the lightpipe structure is applied to different quadrangular surfaces in the U.S. Pat. Nos. 5,303,322 and 5,050,946.
Traffic lights with more depth and bigger dimensions are produced in order to obtain a homogeneous intensity. It may be beneficial to provide thinner combinations of lens and light sources for the light while at the same time obtaining a homogeneous intensity.